The present invention relates to unsymmetrical 2-hydroxy-5-aminobiphenyl derivatives and to colorants for oxidative dyeing of keratin fibers, particularly human hair, based on a developer/coupler combination containing a 2-hydroxy-5-aminobiphenyl derivative as the developer.
In the area of keratin fiber dyeing, particularly hair dyeing, oxidation dyes have attained substantial importance. In this case, the coloration is produced by reaction of certain developers with certain couplers in the presence of an appropriate oxidant. Suitable developers are, in particular, p-phenylenediamines and p-aminophenol, and suitable couplers are, for example, resorcinols, 1-naphthol, 3-aminophenols and m-phenylenediamine.
The oxidation dyes used for dyeing human hair must meet numerous requirements in addition to that of being able to produce colorations of the desired intensity. For example, these dyes must be harmless from a toxicological and dermatological standpoint, and the obtained hair colorations must have good light fastness, resistance to permanent waving, acid fastness and rubbing fastness. In any case, however, such colorations must remain stable over a period of at least 4 to 6 weeks in the absence of exposure to light, rubbing and chemical agents. Moreover, by combination of appropriate developers and couplers, it must be possible to create a wide range of different color shades.
The use of certain symmetrical diaminodihydroxydiphenyls in oxidative hair colorants is known from German Unexamined Patent Application [DE-OS] 25 18 393. These colorants, however, produce only olive-brown to green-gray colorations. Hence, a need continued to exist for novel developers capable of producing a broader range of color shades.
We have now found that blond to red shades can be obtained by coupling a 2-hydroxy-5-aminobiphenyl derivative of general formula (I) with a common coupler.
Hence, the object of the present invention is a colorant for oxidative dyeing of keratin fibers, for example wool, furs, feathers or hair, particularly human hair, based on a developer-coupler combination containing as the developer a 2-hydroxy-5-aminobiphenyl derivative of general formula (I) or a physiologically tolerated water-soluble salt thereof 
wherein
R1 denotes hydrogen, a halogen atom, C1-C4-alkyl group a C1-C4-hydroxyalkyl group, C1-C4-alkoxy group or a C1-C4-hydroxyalkoxy group;
R2, R3, R4, R5, R6 can be equal or different and independently of each other denote hydrogen, a halogen atom, a cyano group, a hydroxyl group, a C1-C4-alkoxy group, a C1-C4-hydroxyalkoxy group, a C1-C6-alkyl group, a C1-C4-alkyl thioether group, a mercapto group, a nitro group, an amino group (NH2), an alkylamino group, a dialkylamino group, a trifluoromethyl group, a xe2x80x94C(O)H group, a xe2x80x94C(O)CH3 group, a xe2x80x94C(O)CF3 group, an xe2x80x94Si(CH3)3 group, a C1-C4-hydroxyalkyl group, a C3-C4-dihydroxyalkyl group, a xe2x80x94CHxe2x95x90CHR7 group, a xe2x80x94(CH2)pxe2x80x94CO2R8 group or a xe2x80x94(CH2)pR9 group, with p=1,2,3 or 4, a xe2x80x94C(R10)=NR11 group, or a C(R12)Hxe2x80x94NR13R14 group, or two adjacent R2 to R6 groups form an xe2x80x94Oxe2x80x94CH2xe2x80x94Oxe2x80x94 bridge;
R7 denotes hydrogen, a hydroxyl group, a nitro group, an amino group, a xe2x80x94CO2R12 group or a xe2x80x94C(O))CH3 group;
R8, R10 and R13 can be equal or different and independently of each other denote hydrogen or a C1-C4-alkyl group;
R9 denotes an amino group or a nitrile group;
R11, R14 and R15 can be equal or different and independently of each other denote hydrogen, a hydroxyl group, a C1-C4-alkyl group, a C1-C4-hydroxyalkyl group, a C3-C4-dihydroxyalkyl group or a radical of formula 
R12 denotes hydrogen, an amino group or a hydroxyl group, provided that the compound of formula (I) does not present a center of symmetry.
Suitable compounds of formula (I) are, for example:
2-hydroxy-3-chloro-5-aminobiphenyl; 2-hydroxy-3-methyl-5-aminobiphenyl; 2-hydroxy-4-chloro-5-aminobiphenyl; 2-hydroxy-4-methyl-5-aminobiphenyl; 2,2xe2x80x2-dihydroxy-5-aminobiphenyl; 2,3xe2x80x2-dihydroxy-5-aminobiphenyl; 2,4xe2x80x2-dihydroxy-5-aminobiphenyl; 2,5xe2x80x2-dihydroxy-5-aminobiphenyl; 2,6xe2x80x2-dihydroxy-5-aminobiphenyl; 2-hydroxy-5,2xe2x80x2-diaminobiphenyl; 2-hydroxy-5,3xe2x80x2-diaminobiphenyl; 2-hydroxy-5,4xe2x80x2-diaminobiphenyl; 2-hydroxy-5,5xe2x80x2-diaminobiphenyl; 2-hydroxy-5,6xe2x80x2-diaminobiphenyl; 2,2xe2x80x2,3xe2x80x2-trihydroxy-5-aminobiphenyl; 2,2xe2x80x2,4xe2x80x2-trihydroxy-5-aminobiphenyl; 2,2xe2x80x2,5xe2x80x2-trihydroxy-5-aminobiphenyl; 2,2xe2x80x2,6xe2x80x2-trihydroxy-5-aminobiphenyl; 2,3xe2x80x2,4xe2x80x2-trihydroxy-5-aminobiphenyl; 2,3xe2x80x2,5xe2x80x2-trihydroxy-5-aminobiphenyl; 2-hydroxy-5,2xe2x80x2,3xe2x80x2-triaminobiphenyl; 2-hydroxy-5,2xe2x80x2,4xe2x80x2-triaminobiphenyl; 2-hydroxy-5,2xe2x80x2,5xe2x80x2-triaminobiphenyl; 2-hydroxy-5,2xe2x80x2,6xe2x80x2-triaminobiphenyl; 2-hydroxy-5,3xe2x80x2,4xe2x80x2-triaminobiphenyl; 2-hydroxy-5,3xe2x80x2,5xe2x80x2-triaminobiphenyl; 2-hydroxy-5,3xe2x80x2,4xe2x80x2-triaminobiphenyl; 2-hydroxy-5,3xe2x80x2,5xe2x80x2-triaminobiphenyl, 2,2xe2x80x2-dihydroxy-5,3xe2x80x2-diaminobiphenyl; 2,2xe2x80x2-dihydroxy-5,4xe2x80x2-diaminobiphenyl; 2,2xe2x80x2-dihydroxy-5,6xe2x80x2-diaminobiphenyl; 2,3xe2x80x2-dihydroxy-5,4xe2x80x2-diaminobiphenyl; 2,3xe2x80x2-dihydroxy-5,5xe2x80x2-diaminobiphenyl; 2,3xe2x80x2-dihydroxy-5,6xe2x80x2-diaminobiphenyl; 2-hydroxy-5-amino-2xe2x80x2-aminomethylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-chlorobiphenyl; 2-hydroxy-5-amino-2xe2x80x2-cyano biphenyl; 2-hydroxy-5-amino-2xe2x80x2-fluorobiphenyl; 2-hydroxy-5-2xe2x80x2-methoxybiphenyl; 2-hydroxy-5-amino-2xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-methylsulfanylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-nitrobiphenyl; 2-hydroxy-5-amino-3xe2x80x2-aminomethylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2-chlorobiphenyl; 2-hydroxy-5-amino-3xe2x80x2-cyanobiphenyl; 2-hydroxy-5-amino-3xe2x80x2-flurobiphenyl; 2-hydroxy-5-amino-3xe2x80x2-methoxybiphenyl; 2-hydroxy-5-amino-3xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2-methylsulfanylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2-nitrobiphenyl; 2-hydroxy-5-amino-4xe2x80x2-aminomethylbiphenyl; 2-hydroxy-5-amino-4xe2x80x2-chlorobiphenyl; 2-hydroxy-5-amino-4xe2x80x2-cyanobiphenyl; 2-hydroxy-5-amino-4xe2x80x2-fluorobiphenyl; 2-hydroxy-5-amino-4xe2x80x2-methoxybiphenyl; 2-hydroxy-5-amino-4xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-4xe2x80x2-methylsulfanylbiphenyl; 2-hydroxy-5-amino-4xe2x80x2-nitrobiphenyl; 2-hydroxy-5-amino-5xe2x80x2-aminomethylbiphenyl; 2-hydroxy-5-amino-5xe2x80x2-chlorobiphenyl; 2-hydroxy-5-amino-5xe2x80x2-cyanobiphenyl; 2-hydroxy-5-amino-5xe2x80x2-fluorobiphenyl; 2-hydroxy-5-amino-5xe2x80x2-methoxybiphenyl; 2-hydroxy-5-amino-5xe2x80x2-methyl-biphenyl; 2-hydroxy-5-amino-5xe2x80x2-methylsulfanybiphenyl; 2-hydroxy-5-amino-5xe2x80x2-nitrobiphenyl; 2-hydroxy-5-amino-6xe2x80x2-amino-methylbiphenyl; 2-hydroxy-5-amino-6xe2x80x2-chlorobiphenyl; 2-hydroxy-5-amino-6xe2x80x2-cyanobiphenyl; 2-hydroxy-5-amino-6xe2x80x2-fluorobiphenyl; 2-hydroxy-5-amino-6xe2x80x2-methoxybiphenyl; 2-hydroxy-5-amino-6xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-6xe2x80x2-methylsulfanylbiphenyl; 2-hydroxy-5-amino-6xe2x80x2-nitrobiphenyl; 2,2xe2x80x2-dihydroxy-5-amino-3xe2x80x2-methylbiphenyl; 2,2xe2x80x2-dihydroxy-5-amino-4xe2x80x2-methylbiphenyl; 2,2xe2x80x2-dihydroxy-5-amino-5xe2x80x2-methylbiphenyl; 2,2xe2x80x2-dihydroxy-5-amino-6xe2x80x2-methylbiphenyl; 2,3xe2x80x2-dihydroxy-5-amino-4xe2x80x2-methylbiphenyl; 2,3xe2x80x2-dihydroxy-5-amino-5xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2,3xe2x80x2-dimethoxybiphenyl; 2-hydroxy-5-amino-2xe2x80x2,3-dimethylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2,4xe2x80x2-dimethoxybiphenyl; 2-hydroxy-5-amino-2xe2x80x2,4xe2x80x2-dimethylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2,5xe2x80x2-dimethoxybiphenyl; 2-hydroxy-5-amino-2xe2x80x2,5xe2x80x2-dimethylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2,6xe2x80x2-dimethoxybiphenyl; 2-hydroxy-5-amino-2xe2x80x2,6xe2x80x2-dimethylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2,4xe2x80x2-dimethoxybiphenyl; 2-hydroxy-5-amino-3xe2x80x2,4xe2x80x2-dimethylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2,5xe2x80x2-dimethoxybiphenyl; 2-hydroxy-5-amino-3xe2x80x2,5xe2x80x2-dimethylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-methoxy-3xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-methoxy-4xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-methoxy-5xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-2xe2x80x2-methoxy-6xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2-methoxy-4xe2x80x2-methylbiphenyl; 2-hydroxy-5-amino-3xe2x80x2-methoxy-5xe2x80x2-methylbiphenyl; 4-amino-2-benzo-[1,3]dioxol-5-ylphenol; 4-amino-2-benzo[2,4]dioxol-5-ylphenol and 2-hydroxy-5-amino-4xe2x80x2-(2-hydroxyethoxy)biphenyl.
Particularly preferred are compounds of formula (I) wherein (i) R1 denotes hydrogen or (ii) four of the R2 to R6 groups denote hydrogen while the fifth group denotes hydrogen, a methyl group, an amino group, a hydroxyl group, a C1-C4-hydroxyalkyl group or a methoxy group, or (iii) the groups R1 to R6 at the same time denote hydrogen, or (iv) R1 denotes hydrogen and four of the R2 to R6 groups denote hydrogen while the fifth group denotes hydrogen, a methyl group, an amino group, a hydroxyl group, a C1-C4-hydroxyalkyl group or a methoxy group.
Outstandingly suitable 2-hydroxy-5-aminobiphenyl derivatives of formula (I) in terms of the overall invention are 2-hydroxy-5-aminobiphenyl; 2,4xe2x80x2-dihydroxy-5-aminobiphenyl, 2-hydroxy-5-amino-4xe2x80x2-(2xe2x80x3-hydroxyethoxy)biphenyl, 2,4xe2x80x2-dihydroxy-5-amino-2xe2x80x2-methylbiphenyl, 2-hydroxy-5-amino-4xe2x80x2-(2xe2x80x3-hydroxyethyl)biphenyl, 2-hydroxy-5,4xe2x80x2-diaminobiphenyl or physiologically tolerated salts thereof.
The compounds of formula (I) can be used either as free bases or in the form of their physiologically tolerated salts with inorganic or organic acids, for example hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, propionic acid, lactic acid or citric acid.
The 2-hydroxy-5-aminobiphenyl derivative of formula (I) is contained in the colorant of the invention in an amount from about 0.005 to 20 wt. %, an amount from about 0.01 to 5.0 wt. % and particularly from 0.1 to 2.5 wt. % being especially preferred.
Preferred couplers are 2,6-diaminopyridine, 2-amino-4-[(2-hydroxyethyl)amino]anisole, 2,4-diamino-1-fluoro-5-methylbenzene, 2,4-diamino-1-methoxy-5-methylbenzene, 2,4-diamino-1-ethoxy-5-methylbenzene, 2,4-diamino-1-(2-hydroxyethoxy)-5-methylbenzene, 2,4-di-[(2-hydroxyethyl)amino]-1,5-dimethoxybenzene, 2,3-diamino-6-methoxypyridine, 3-amino-6-methoxy-2-(methylamino)pyridine, 2,6-diamino-3,5-dimethoxypyridine, 3,5-diamino-2,6-dimethoxypyridine, 1,3-diaminobenzene, 2,4-diamino-1-(2-hydroxyethoxy)benzene, 2,4-diamino-1,5-di-(2-hydroxyethoxy)benzene, 1-(2-aminoethoxy)-2,4-diaminobenzene, 2-amino-1-(2-hydroxyethoxy)-4-methylaminobenzene, 2,4-diaminophenoxyacetic acid, 3-[di-(2-hydroxyethyl)amino]-aniline, 4-amino-2-di-[(2-hydroxyethyl)amino]-1-ethoxybenzene,5-methyl-2-(1-methylethyl)phenol, 3-[(2-hydroxyethyl)amino]aniline,3-[(2-aminoethyl)amino]aniline, 1,3-di-(2,4-diaminophenoxy)propane,di-(2,4-diaminophenoxy)methane, 1,3-diamino-2,4-dimethoxybenzene, 2,6-bis-(2-hydroxyethyl)aminotoluene, 4-hydroxyindole, 3-dimethylaminophenol, 3-diethylaminophenol, 5-amino-2-methylphenol, 5-amino-4-fluoro-2-methylphenol, 5-amino-4-methoxy-2-methylphenol, 5-amino-4-ethoxy-2-methylphenol, 3-amino-2,4-dichlorophenol, 5-amino-2,4-dichlorophenol, 3-amino-2-methylphenol, 3-amino-2-chloro-6-methylphenol, 3-aminophenol, 2-[(2-hydroxyphenyl)amino]acetamide, 5-[(2-hydroxyethyl)amino]-2-methylphenol, 3-[(2-hydroxyethyl)amino]phenol, 3-[(2-methoxyethyl)amino]phenol, 5-amino-2-ethylphenol, 2-(4-amino-2-hydroxyphenoxy)ethanol, 5-[(3-hydroxypropyl)amino]-2-methylphenol, 3-[(2,3-dihydroxypropyl)amino]-2-methylphenol, 3-[(2-hydroxyethyl)amino]-2-methylphenol, 2-amino-3-hydroxypyridine, 5-amino-4-chloro-2-methylphenol, 1-naphthol, 1,5-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 2-methyl-1-naphthol acetate, 1,3-dihydroxybenzene, 1-chloro-2,4-dihydroxybenzene, 2-chloro-1,3-dihydroxybenzene, 1,2-dichloro-3,5-dihydroxy-4-methylbenzene, 1,5-dichloro-2,4-dihydroxybenzene, 1,3-dihydroxy-2-methylbenzene, 3,4-methylenedioxyphenol, 3,4-methylenedioxyaniline, 5-[(2-hydroxyethyl)amino]-1,3-benzodioxol, 6-bromo-1-hydroxy-3,4-methylenedioxybenzene, 3,4-diaminobenzoic acid, 3,4-dihydro-6-hydroxy-1,4(2H)-benzoxazine, 6-amino-3,4-dihydro-1,4(2H)benzoxazine, 3-methyl-1-phenyl-5-pyrazolone, 5,6-dihydroxyindole, 5,6-dihydroxyindoline, 5-hydroxyindole, 6-hydroxyindole, 7-hydroxyindole and 2,3-indolinedione.
Although the advantageous properties of the 2-hydroxy-5-aminobiphenyl derivatives of formula (I) described here suggest that said derivatives should be used as the only developers, it is, of course, also possible to use the 2-hydroxy-5-aminobiphenyl derivatives of formula (I) together with known developers such as, for example, 1,4-diaminobenzene, 2,5-diaminotoluene, 2,5-diaminophenylethyl alcohol, 4-aminophenol and the derivatives thereof, for example 4-amino-3-methylphenol, 4,5-diaminopyrazole derivatives, for example 4,5-diamino-1-(2-hydroxyethyl)pyrazole, or tetraaminopyrimidines.
The couplers and developers can be contained in the colorants of the invention either alone or in admixture with each other, the total amount of couplers and developers in the colorants of the invention (based on the total amount of colorant) being in all cases from about 0.005 to 20 wt. %, preferably from about 0.01 to 5.0 wt. % and particularly from 0.1 to 2.5 wt. %.
The total amount of developer-coupler combination contained in the colorants described herein is preferably from about 0.01 to 20 wt. %, an amount from about 0.02 to 10 wt. % and particularly from 0.2 to 6.0 wt. % being especially preferred. In general, the developers and couplers are used in approximately equimolar amounts. It is not disadvantageous in this respect, however, if the developers are present in a certain excess or deficiency (for example in a coupler: developer ratio from 1:2 to 1:0.5.
Moreover, the colorants of the invention can additionally contain other components, for example 6-amino-2-methylphenol and 2-amino-5-methylphenol, as well as other common direct dyes from the group consisting of acid and basic dyes, triphenylmethane dyes, anthraquinone dyes, aromatic nitro dyes, azo dyes, food dyes or disperse dyes.
The colorants can contain these dye components in an amount from about 0.1 to 4.0 wt. %.
Naturally, the couplers and developers and the other dye components, as long as they are bases, can also be used in the form of physiologically tolerated salts of organic or inorganic acids, for example hydrochloric acid or sulfuric acid orxe2x80x94providing that they contain aromatic OH groupsxe2x80x94in the form of salts of bases, for example as alkali metal phenoxides.
Moreover, if the colorants are to be used for coloring hair, they can contain other common cosmetic additives, for example antioxidants such as ascorbic acid, thioglycolic acid or sodium sulfite, as well as perfume oils, complexing agents, wetting agents, emulsifiers, UV absorbers, thickeners and hair-care agents. The colorant of the invention can be a solution, particularly an aqueous or aqueous-alcoholic solution. A particularly preferred formulation form, however, is a cream, gel or emulsion. Such a composition consists of a mixture of the dye components and the usual additives employed for such preparations.
Common additives to solutions, creams, emulsions or gels are, for example, solvents such as water, lower aliphatic alcohols, for example ethanol, propanol or isopropanol, glycerol or glycols such as 1,2-propylene glycol, moreover wetting agents or emulsifiers from the classes of anionic, cationic, amphoteric or nonionic surface-active agents, for example fatty alcohol sulfates, ethoxylated fatty alcohol sulfates, alkylsulfonates, alkylbenzenesulfonates, alkyltrimethylammonium salts, alkylbetaines, ethoxylated fatty alcohols, ethoxylated nonylphenols, fatty acid alkanolamides and ethoxylated fatty esters, furthermore thickeners such as the higher fatty alcohols, starch, cellulose derivatives, petrolatum, paraffin oil and fatty acids, also hair-care agents such as cationic resins, lanolin derivatives, cholesterol, pantothenic acid and betaine. The cited constituents are used in amounts commonly employed for such purposes, for example the wetting agents and emulsifiers at a concentration of about 0.5 to 30 wt. %, the thickeners in an amount from about 0.1 to 25 wt. % and the hair-care agents at a concentration from about 0.1 to 5.0 wt. %.
Depending on the composition, the colorants of the invention can be weakly acidic, neutral or alkaline. In particular, they have a pH of about 6.5 to 11.5. Adjustment to a basic pH is preferably done with ammonia, but it can also be done with an organic amine, for example monoethanolamine or triethanolamine, or with an inorganic base such as sodium hydroxide or potassium hydroxide. Suitable for adjustment to an acidic pH are inorganic or organic acids, for example phosphoric acid, acetic acid, citric acid or tartaric acid.
For oxidative dyeing of hair, the afore-described colorants are mixed with an oxidant just before use, and the resulting mixture is applied to hair in an amount sufficient for the hair-dyeing treatment, in general about 60 to 200 grams, depending on the hair fullness.
Suitable oxidants for developing the hair coloration are mainly hydrogen peroxide or its compounds of addition to urea, melamine, sodium borate or sodium carbonate, in the form of a 3-12%, preferably 6% aqueous solution, atmospheric oxygen also being suitable. When a 6% hydrogen peroxide solution is used as oxidant, the weight ratio of hair colorant to oxidant is from 5:1 to 1:2, but preferably 1:1. Larger amounts of oxidant are used primarily at higher dye concentrations in the hair colorant or when strong bleaching of the hair is wanted at the same time. The mixture is allowed to act on the hair at 15 to 50xc2x0 C. for about 10 to 45 min, preferably 30 min, after which the hair is rinsed with water and dried. Optionally, following this rinsing, the hair is washed with a shampoo and optionally post-rinsed with a weak organic acid, for example citric acid or tartaric acid. The hair is then dried.
The colorants of the invention containing a 2-hydroxy-5-aminobiphenyl derivative of formula (I) give hair colorations of excellent color fastness, particularly in terms of light fastness, wash fastness and rubbing fastness. As far as the dyeing properties are concerned, the hair colorants of the invention provide a wide range of different color shades from blond to brown, purple, violet and even blue and black, depending on the type and composition of the dye components. Such color shades are characterized by unusual color intensity. The very good coloring properties of the colorant of the present invention also manifest themselves in that these colorants make it possible to dye graying hair, chemically not previously damaged, without any problems and with good covering power. The 2-hydroxy-5-aminobiphenyl derivatives of formula (I) are water-soluble and give colorations of high intensity and excellent color fastness, particularly in terms of light fastness, wash fastness and rubbing fastness. They also have excellent storage stability, particularly as components of the aforedescribed colorants.
Another object of the present invention are novel 2-hydroxy-5-aminobiphenyl derivatives of formula (Ia) or physiologically tolerated, water-soluble salts thereof 
wherein
R1 denotes hydrogen, a halogen atom, a C1-C4-alkyl group, a C1-C4-hydroxyalkyl group, a C1-C4-alkoxy group or a C1-C4-hydroxyalkoxy group;
R2, R3, R4, R5, R6 can be equal or different and independently of each other denote hydrogen, a halogen atom, a cyano group, a hydroxyl group, a C1-C4-alkoxy group, a C1-C4-hydroxyalkoxy group, a C1-C6-alkyl group, a C1-C4-alkyl thioether group, a mercapto group, a nitro group, an amino group, an alkylamino group, a dialkylamino group, a trifluoromethyl group, a xe2x80x94C(O)H group, a xe2x80x94C(O)CH3 group, a xe2x80x94C(O)CF3 group, an xe2x80x94Si(CH3)3 group a C1-C4-hydroxyalkyl group, a C3-C4-dihydroxyalkyl group, a xe2x80x94CHxe2x95x90CHR7 group, a xe2x80x94(CH2)pxe2x80x94CO2R8 group or a xe2x80x94(CH2)pxe2x80x94R9 group with p=1,2,3 or 4, a xe2x80x94C(R10)=NR11 group or a C(R12)Hxe2x80x94NR13R14 group, or two adjacent R2 to R6 groups form an xe2x80x94Oxe2x80x94CH2xe2x80x94Oxe2x80x94 bridge;
R7 denotes hydrogen, a hydroxyl group, a nitro group, an amino group, a CO2R12 group, or a xe2x80x94C(O)CH3 group;
R8, R10 and R13 can be equal or different and independently of each other denote hydrogen or a C1-C4-alkyl group;
R9 denotes an amino or nitrile group;
R11, R14 and R15 can be equal or different and independently of each other denote hydrogen, a hydroxyl group, a C1-C4-alkyl group, a C1-C4-hydroxyalkyl group, a C3-C4-dihydroxyalkyl group or a radical of formula 
R12 denotes hydrogen, an amino group or a hydroxyl group, provided that the compound of formula (I) has no center of symmetry and that group R2 does not denote hydrogen or a hydroxyl group.
The 2-hydroxy-5-aminobiphenyl derivatives of formula (I) can be prepared by use of known methods of synthesis, for example methods similar to the general methods described in the following preparative examples.
The following examples illustrate the invention in greater detail without limiting its scope.